Composite restorations degrade during wear, but it is unknown how wear affects the composite surface and influences composite-to-composite bonding in minimally invasive repair. Here, it is hypothesized that in vitro exposure of composites to oral biofilm yields clinically relevant degradation of composite surfaces, and its influence on composite-to-composite bonding is determined. Biofilms on composite surfaces in vitro increased their roughness and decreased filler particle exposure, except for a microhybrid composite, similar to effects of clinical wear in palatal appliances. Failure shear stresses after intermediate-adhesive-resin application were significantly lower after aging by in vitro exposure to biofilms, while silica-coating maintained the same failure stress levels as in non-aged composites. Failure modes were predominantly cohesive after silica-coating, while intermediate-adhesive-resin application yielded more adhesive failure. It is concluded that in vitro exposure to oral biofilm is a clinically relevant aging condition, and that silica-coating is to be preferred for the repair of aged composites.